Adding Ibrance (palbociclib) to standard endocrine therapy failed to prolong the time women with early hormone receptor (HR)-positive, human epidermal growth factor (HER2)-negative breast cancer lived without having their disease return or spread, according to data from a Phase 3 trial.
The study, called PENELOPE-B (NCT01864746), was designed to assess if the addition of Ibrance with five years of standard adjuvant endocrine therapy would be superior to a placebo plus standard hormone therapy at prolonging the time women lived without having their cancer spread or return — a parameter known as invasive disease-free survival (iDFS). Adjuvant therapy is a treatment normally given after surgery to prevent cancer from returning.
Sponsored by The German Breast Group (GBG) as part of a clinical research collaboration with Pfizer and other study groups, PENELOPE-B enrolled a total of 1,250 pre- and post-menopausal women from more than 190 clinical sites across 12 countries.
Following enrollment, women were randomly assigned to receive a 125 mg daily oral dose of Ibrance or a placebo from day 1 to day 21 followed by seven days off treatment (or placebo) in a 28-day cycle, for a total of 13 cycles.
All women participating in the study continued showing signs of residual disease after undergoing neoadjuvant chemotherapy and had a high risk of cancer relapse. Neoadjuvant therapy is a treatment given to shrink a tumor before a patient undergoes cancer removal surgery.
Full data from PENELOPE-B will be presented at an upcoming medical congress.
“Reducing the risk of disease recurrence in patients who have residual disease after neoadjuvant chemotherapy is a complex clinical challenge,” Sibylle Loibl, MD, PhD, professor and chair of GBG, said in a press release. “Despite this outcome, we believe that key learnings will emerge from the large number of biomarkers being analyzed from collected tumor tissue, which will help inform future breast cancer research.”
Marketed by Pfizer, Ibrance is a selective inhibitor of cyclin-dependent kinase (CDK) 4/6, which are enzymes that, when overactive, can promote the proliferation and growth of cancer cells. By inhibiting these enzymes, Ibrance aims to halt the uncontrolled growth of malignant breast cancer cells.
Although not indicated for early breast cancer, Ibrance is currently approved in more than 95 countries and has been prescribed to nearly 340,000 patients worldwide.
In the U.S., the medication has been approved to be used in combination with an aromatase inhibitor as initial hormonal therapy to treat post-menopausal women or men with advanced or metastatic, HR-positive, HER2-negative breast cancer.
Ibrance is also approved to be used in combination with AstraZeneca’s Faslodex (fulvestrant) to treat patients with advanced or metastatic HR-positive, HER2-negative breast cancer whose disease progressed following hormone therapy.
“This is the first randomized Phase 3 study to establish mature iDFS results for a CDK4/6 inhibitor as part of the adjuvant treatment for early breast cancer,” Chris Boshoff, MD, PhD, Pfizer’s chief development officer of oncology, said. “While we are disappointed with this result, we look forward to continuing to work with our research partners to understand subgroup data and how these could inform the development of our next-generation CDK inhibitors in early breast cancer.”
“We are proud of the transformative impact Ibrance has had on the treatment of HR+, HER2- metastatic breast cancer — a vastly different treatment setting than early breast cancer,” he added. “Our commitment to the metastatic patient community is as strong as ever as we continue to generate new data, including the most extensive body of real-world evidence for a CDK4/6 inhibitor.”
In addition to PENELOPE-B, another Phase 3 trial called PALLAS (NCT02513394) has been investigating Ibrance’s therapeutic potential in patients with early breast cancer, when given alongside hormone therapy.
Recently, an independent data monitoring committee overseeing the study deemed it would be unlikely the addition of Ibrance to conventional hormone therapy would be superior to standard therapy alone at delaying or preventing cancer spread in these patients.
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